The purpose of body armor is to stop a high velocity projectile. Currently, the best known method of stopping a projectile is to have it fly against a plate that comprises a tile and a backing material.
One method that is typically used in the prior art to form the tile is reaction bonding. In one example, micron-sized silicon carbide or boron carbide powder is mixed with silicon powder and carbon black powder. The mixture is then put in a form, then placed in a high temperature oven, where the silicon is melted in order to have the silicon react at high temperature with the carbon to form silicon carbide and surround the silicon carbide or boron carbide particles with the silicon carbide particles. This concept is similar to the making of concrete.
Another method that is typically used in the prior art is the standard sintering of silicon carbide. Micron-sized silicon carbide particles are sintered together under high temperature to form a solid tile of about 99% density.
Silicon carbide and boron carbide are typically used because they have what is known in the industry as high hardness, meaning they are very good at stopping projectiles. However, they exhibit low fracture toughness, meaning that they are extremely brittle and are not good at resisting fracture when they have a crack. Therefore, although tiles made from these materials can slow down and stop a high velocity projectile, such as a bullet, they often shatter in the process and are only good for a single hit.
It is desirable to form a material that is harder, but that also is higher in fracture toughness. However, that concept is a contradiction is terms. Currently, the higher the fracture toughness of a material, the more that material becomes metal-like, which means less brittle and more ductile. The higher the hardness of the material, the lower the ductility and the higher the brittleness. FIG. 1 illustrates a graph that plots the fracture toughness versus the hardness (measured in hardness Vickers) of different materials. As can be seen, aluminum comprises a high fracture toughness of 10, but a low hardness value of 130. In comparison, a material that is formed from micron-sized silicon carbide or boron carbide powder that has been put through a conventional sintering process exhibits a high hardness value of 2000, but a low fracture toughness value of between 2 and 4. The problem of the prior art is evident by the trend line, which supports the concept that the harder a material becomes, the lower the fracture toughness it comprises, and the higher fracture toughness a material has, the softer that material becomes.